Lecture08 Mobile Positioning and LBS 第 8 讲 移动定位与服务
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Transcript of Lecture08 Mobile Positioning and LBS 第 8 讲 移动定位与服务
Lecture08 Mobile Positioning and LBS
第 8 讲 移动定位与服务§8.1 LBS Basics
§8.2 LBS Technologies
§8.3 Mobile Positioning
§8.4 Geographic Information System
Location Based Services (LBS)
What is it? Allow you to report real time current location to a given platform
Information service accessible using mobile devices through mobile network
Ability to make use of geographical position of mobile device
Why need it ?Location is important
Evolution of LBS
First generationManually input location info.
E.g. zip code, a city name or street address.
Customized contentE.g. driving directions, nearby restaurant or store locations, or weather information.
Second generationAutomatically determine location info.
Usually accurate to within a few kilometers (1 to 2 miles), similar accuracy as in first-generation applications.
Similar services to those in first-generation applications.
Evolution of LBS
Third generationCan obtain more accurate location info.
Can initiate services based on location.
Can provide timely updatesnearby brick-and-mortar services,
asset tracking information, and
street-level mapping and routing.
Feature-rich and user-friendly
LBS Applications
What are the top uses? Emergency servicesGPS Navigation Weather alerts Traffic updates Find-it servicesWireless advertisingAccess controlSocial networking
Notable players Google Maps Foursquare Facebook Places 街旁
§8.2 LBS Technologies
LBS App.
Location Management
Localization Module
Geographic Information
System
LBS Technologies
Localizing or Positioning MethodsGlobal Positioning System (GPS)
Cellular, WiFi, NFC, RFID, Bluetooth � Geographic Information Systems (GIS)
Provide tools to provision and administer base map data
Manage point-of-interest data Location Management
Process positioning and GIS data
Acts as gateway between positioning equipment and LBS infrastructure
LBS System based on GSM
Mobile Positioning System of GSM
Specified by ANSI and ETSI Extend classical GSM system Hardware and Software
LMU: Location Measurement UnitTo measure the time difference between BSs
MLC: Mobile Location CenterSMLC: Service MLC
Measurement and calculation
GMLC: Gateway MLCInterface to others
Mobile Positioning System of GSM
图 9-10 , p262
Mobile Positioning System of GSM
MTGMLC GMLCauth.HLR GMLCloc. req.MT/VLR MT/VLRloc. rep.GMLC
WebSphere LBS
Location Component
To collect and process client location records
§8.3 Mobile Positioning
PositioningTo capture the location of a mobile device
Considerations: Accuracy vs. Cost Categories: based on where the calculation is done
Network-basedFor both new and legacy handsets.Quite cost-effectiveLow accuracy: from hundred meters to several kilometers
Terminal-based High accuracy: several metersHigh cost, for both the terminal and network.
Cell Identity
A naive solution Location of BS Location of MT Accuracy
Depending on the density and coverage of BS
~100m to ~10km
Timing Advance (TA)
TA: The time of a round trip between base station and mobile terminal.Usually between 0 and 63 bit period (~ 3.69 microseconds).
TA distance1 bit 550m63 × 550m 35km
Pros and consLow accuracy: 0.2~10km
Multipath fading
Simple: no change at MT, minor change at BS
CGI + TA
Cell Global Identity, CGIA standard identifier for mobile phones cells
TA: within a cell CGI+TA: global
Time of Arrival (TOA)
d = v * t Distance values to >3 base stations High accuracy
100~150m High complexity
Synchronization among BSs
Special LMU
Computation Work flow
MT sends to BSs
Each BS measures time
Time Difference of Arrival (TDOA)
TDOA = TOA1 – TOA2
Angle Of Arrival (AOA)
Input data: Angle with two BSs,
Distance between the two BSs Two BSs for 2D location Three BSs for 3D location Need special antenna
Multipath Fingerprinting
RF pattern match Based on the characteristics of multipath signal Collecting fingerprinting
Dedicated learning phase
Store the fingerprint in a database Locating mobile device
collect the current signal pattern
Match it with those in database
Mobile Terminal based Positioning
More accuracy than network-based technologies Terminal participant in the location calculation Suitable for 3rd generation of LBS Popular technologies
E-OTD: uses BSs
GPS: uses satellites.
Enhanced Observed Time Difference (E-OTD)
TOA at mobile terminal But the MT makes the time measurements instead of BS
Enhanced Observed Time Difference (E-OTD)
Values to measureOTD: observed time difference
RTD: real time difference
GTD: geographic time difference
Global Positioning System (GPS)
HistoryFeasibility studies begun in 1960’s.
First satellite launched in 1978.
System declared fully operational in April, 1995. Consists of 24 MEO satellites that transmit precise
microwave signalsAbout 20,200km above the Earth’s surface.
Control Segment
Space Segment
User Segment
Monitor Stations
GroundAntennas
Master Station
Three Segments of GPS
Four Basic Functions of GPS
Position and coordinates.
The distance and direction between any two waypoints, or a position and a waypoint.
Travel progress reports.
Accurate time measurement.
Position Is based on Time
T + 3
Distance between satellite and receiver = “3 times the speed of light”
TSignal leaves satellite at time “T”
Signal is picked up by the receiver at time “T + 3”
The satellites constantly broadcast signals that can be read by GPS-enabled devices.Line of sight : suitable for outdoor only
Three Satellites (2D Positioning)
Three Dimensional (3D) Positioning
GPS
Accuracy5m-40m
Highly relying on the accuracy of clockAtomic clock at each satellite
1ms300km
LimitationsLine of sight to the satellites outdoor only
Solution: Backup method: cell based ones
Long delay of positioning: 20s-40s
A-GPS
Network-assisted GPS GPS + assistance from Additionally uses network resources to locate and use
the satellites in poor signal conditions. To alleviate both restrictions of GPS
Assistance of Location Server in A-GPS
Information used to more quickly acquire satellitesIt can supply information of GPS satellites, enabling the GPS receiver to lock to the satellites more rapidly.
The network can provide precise time.
Calculation of position by the server using information from the GPS receiver
The assistance server has a good satellite signal, and plentiful computation power, so it can compare fragmentary signals relayed to it.
Accurate, surveyed coordinates for the cell site towers allow better knowledge of conditions affecting the GPS, enabling more precise calculation of position.
Comparisons
CGI+TA AOA TOA/TDOA E-OTD A-GPS
定位精度 100m~1.1km <125m 50~200m 50~125m 5~50m
使用区域 无限制 无限制 乡村以上 乡村以上 城市
响应时间 3s 10s 10s 5s 1s
设备升级 无 网络、天线
网络 网络、终端 网络、终端
建设成本 低 高 高 高 高
建设周期 短 短 长 长 短
§8.4 Geographic Information System
GIS, mapping software that Relates the location information with other pertinent information to give it meaning and value.
Such as building locations, street layouts, population densities, and a plethora of other information.
A GIS can provide information and insight to both mobile users and people at fixed locations.
GIS
Common Uses of GIS
Uses the location coordinates provided by positioning technologies to give details that are relevant to the user at that specific moment.
Finding what is nearby Routing information Information alerts Mapping densities Mapping quantities
A Summary
ConceptsLBSMobile device positioning
Mobile positioning system Positioning technologies
Network-basedCGI, TA, CGI+TATOA, TDOAAOAFingerprint
Terminal-basedE-OTDGPS, A-GPS